1. Field of the Invention
The present invention relates to photosensitive printing plates, a method of preparing the plates, and also a method of processing the plates. More particularly, the invention relates to a photosensitive printing plate having (1) a layer containing particles of photosensitive silver halide grains coated with a hydrophilic polymer dispersed in an oleophilic polymer and (2) directly on layer (1) a layer of a photosensitive resin composition, the printing plate having a high sensitivity in terms of camera speed, and also a method of preparing and a method of processing such a printing plate.
By the term "a photosensitive printing plate having a high sensitivity in terms of camera speed" or "photosensitive printing plate with camera speed sensitivity" is meant that the photosensitive material is highly sensitive photographically to such an extent that the photosensitive material can be imagewise exposed by focusing an image of an original on the photosensitive layer of the photosensitive material through a focusing lens system using a camera. On the other hand, by the term "a photosensitive printing plate having a contact speed sensitivity" or "photosensitive printing plate with contact speed sensitivity" is meant that the photosensitive material has a sensitivity such that the photosensitive material can be exposed to light to which the photosensitive compound in the photosensitive layer is sensitive through a transparent photographic positive or negative image as an original in contact with the photosensitive material.
The majority of photosensitive printing plates which are commercially used at present are those having a contact speed sensitivity. Since photosensitive printing plates having a contact speed sensitivity require a transparent photographic negative or positive for making printing plates and thus in the case of using such photosensitive printing plates, the number of steps required for making printing plates is larger than those in the case where no transparent photographic negative or positive is required.
Conventional photosensitive compounds used for photosensitive printing plates, in particular, negative working printing plates are diazo compounds or photosensitive polymers such as, for example, polyvinyl cinnamate, but these compounds have a very low photographic sensitivity and hence are unsuitable as photosensitive compounds for photosensitive printing plates having a camera speed sensitivity. In other words, the majority of conventional photosensitive printing plates have a contact speed sensitivity as described above.
The most general photosensitive compounds for photographic materials having a camera speed sensitivity are silver halide and photosensitive printing plates having silver halide emulsion layers have now been produced but these known photosensitive printing plates having a camera speed sensitivity require comparatively complicated processing operations and further they have a low printing life, that is, the number of prints which can be obtained from these photosensitive printing plates is not very large.
Other examples of photosensitive printing plates having a camera speed sensitivity are composite type photosensitive printing plates each comprising a support having formed thereon a photosensitive layer with a contact speed sensitivity (hereinafter, this layer is referred to as the first photosensitive layer) and a silver halide emulsion layer with a camera speed sensitivity (hereinafter, this layer is referred to as the second photosensitive layer) as described in the specifications of Japanese Patent Publication Nos. 13,128/1965 and 23,721/1972; U.S. Pat. Defensive Publication No. T-870,022; and French Pat. No. 2,151,182.
However, in these composite type photosensitive printing plates, the first photosensitive layer with a contact speed sensitivity has poor adhesive properties to the hydrophilic silver halide emulsion layer with a camera speed sensitivity due to the oleophilic property thereof and thus it has been proposed to form an interlayer or a subbing layer having good adhesive properties to both layers between the layers as disclosed in the specifications of, for instance, U.S. Pat. Defensive Publication No. T-870,022 and Japanese Patent Publication No. 23,721/1972. However, the presence of such an interlayer causes the production process of the photosensitive printing plates to be complicated.
Another attempt for improving the adhesive properties between the first photosensitive layer and the second photosensitive layer is disclosed in the specifications of Japanese Patent Publication No. 13,128/1965 and French Pat. No. 2,151,182 and in these descriptions, an interlayer is not employed but it is well known that in such case the silver halide emulsion layer is stripped from the oleophilic surface of the second photosensitive layer in processing the silver halide emulsion layer, which makes the use of such photosensitive printing plates unpractical.
Also, these composite type photosensitive printing plates are generally processed as follows; that is, the silver halide emulsion layer is first imagewise exposed followed by silver halide development to form a silver image and then the first photosensitive layer is exposed to ultraviolet rays through the silver image formed thereon. Then, after removing the silver halide emulsion layer, the first photosensitive layer is developed. In other words, in order to process these composite type photosensitive printing plates, a step of removing the second photosensitive layer and a step of developing the first photosensitive layer are required.